7. (a) Which of these is a non-renewable source of energy? A geothermal B natural gas C tidal D solar (b) Explain why renewable sources provide an increasing fraction of the electricity supply for many countries - Edexcel - GCSE Physics - Question 7 - 2018 - Paper 1

Renewable sources such as wind, solar, and hydroelectric power are being increasingly utilized due to their sustainability and lower environmental impact. As technology improves, the efficiency and cost-effectiveness of these sources rise, leading to a decrease in reliance on non-renewable sources like coal and oil. Additionally, many countries are implementing policies to reduce carbon emissions, promoting the shift towards renewable energy.

To calculate the minimum height, we can use the formula for gravitational potential energy (GPE): $ext{GPE} = mgh$ where:

• m = mass of water = 7.0 kg
• g = gravitational acceleration = 10 m/s²
• h = height (unknown)

Setting GPE equal to the kinetic energy: $1300 = 7.0 imes 10 imes h$ Rearranging gives: $h = \frac{1300}{7.0 \times 10} = 18.57\ m$ Therefore, the minimum height is approximately 18.57 m.

To find the speed of the water, we can use the formula for kinetic energy (KE): $KE = \frac{1}{2} mv^2$ where:

• m = mass of water = 8.0 kg
• KE = 1100 J

Rearranging for speed (v): $v = \sqrt{\frac{2 \times KE}{m}}$ Substituting: $v = \sqrt{\frac{2 \times 1100}{8.0}} = \sqrt{275} \approx 16.58\ m/s$ Thus, the speed of the moving water as it enters the turbine is approximately 16.58 m/s.

To calculate the percentage of kinetic energy transferred, we need to find the kinetic energy before and after passing through the turbine on the graph:

• Kinetic energy before (at 15 m/s): 8 kJ
• Kinetic energy after (at 13 m/s): 6 kJ

The energy transferred to the turbine is: $\text{Energy Transferred} = 8 kJ - 6 kJ = 2 kJ$

Now, the percentage transferred is calculated by: